Development of testing and analysis methodology to assess the long term durability of polymeric composites at high temperatures

A workshop was held to help assess the state-of-the-art in evaluating the long term durability of polymeric matrix composites (PMCs) and to recommend future activities. Design and evaluation of PMCs at elevated temperatures were discussed. The workshop presentations, the findings of the workshop sessions are briefly summarized

Polymer- and Hybrid-Based Biomaterials for Interstitial, Connective, Vascular, Nerve, Visceral and Musculoskeletal Tissue Engineering

In this review, materials based on polymers and hybrids possessing both organic and inorganic contents for repairing or facilitating cell growth in tissue engineering are discussed. Pure polymer based biomaterials are predominantly used to target soft tissues. Stipulated by possibilities of tuning the composition and concentration of their inorganic content, hybrid materials allow to mimic properties of various types of harder tissues. That leads to the concept of “one-matches-all” referring to materials possessing the same polymeric base, but different inorganic content to enable tissue growth and repair, proliferation of cells, and the formation of the ECM (extra cellular matrix). Furthermore, adding drug delivery carriers to coatings and scaffolds designed with such materials brings additional functionality by encapsulating active molecules, antibacterial agents, and growth factors. We discuss here materials and methods of their assembly from a general perspective together with their applications in various tissue engineering sub-areas: interstitial, connective, vascular, nervous, visceral and musculoskeletal tissues. The overall aims of this review are two-fold: (a) to describe the needs and opportunities in the field of bio-medicine, which should be useful for material scientists, and (b) to present capabilities and resources available in the area of materials, which should be of interest for biologists and medical doctors.</jats:p

Damage and Degradation Study of FRP Composites

The present experimental study aims at assessing the different effects of the varying environments on the mechanical properties of FRP composites. The mechanical performance of a composite material is decisively controlled by the state of fiber-matrix interface . Its properties influence the integrity of composite behavior because of its role in transferring stress between the fiber and the matrix. The factors affecting the interface are too complex to be precisely concluded. Fibrous composites are increasingly being used in many casual as well as critical applications owing to various desirable properties including high specific strength, high specific stiffness and controlled anisotropy. But unfortunately polymeric composites are susceptible to heat and moisture when operating in changing environmental conditions. Samples of several Glass-Epoxy composites were manufactured using the traditional hand layup method where the stacking of the plies were alternate and the weight fraction of fiber and matrix was kept at 40-60%.Specimens were cut according to the ASTM D 2344-84(1989) standards. Some of the specimens were kept in the As-cured condition so as to obtain the base properties. Experimental studies have been carried out to study the effects of thermal ageing, liquid nitrogen temperature, thermal shocks, sea and distilled water. Also, tests have been performed to study the effect of ultraviolet rays and microwave conditions on the mechanical behavior of Glass-epoxy composites. The specimens were divided into groups. One group was subjected to cryogenic conditions at -750C for 3 hours and 6 hours. Another group was subjected to elevated temperature at +750C for 5 hours and 10 hours. A separate group samples were immersed in the two mediums separately namely sea water , distilled water at their boiling temperatures .Of the remaining samples a group of samples were kept in a microwave oven for 60 , 90 and 120 secs. whereas the other part of it was kept in a ultraviolet chamber for a period of 100 hrs. Thermal shocks of two types, up-cycle (lower to higher temperature immersion) and down-cycle (higher to lower temperature immersion) were applied The aged samples were subjected to 3-point short beam shear tests. The tests were performed at room temperature with 1 mm/min and 500 mm/min crosshead speeds. The weakening effects were sensitive to loading rate. The ILSS(shear strength) values were then compared with the base values of as cured specimen SEM analysis was done to ascertain the mode of failure

The Use of Poly(vinyl alcohol)-based Hydrogels in Biomedical Applications

Polymers have found increasing favor in biomedical applications due to the greater control that researchers can exert over their properties. Researchers have focused on the development of therapies using biologically compatible polymers due to their ability to limit potentially harmful interactions with the body. This research has led to advances in tissue engineering, controlled and targeted drug delivery, and other biomedical fields, with the goal of improving both the effectiveness and accessibility of health care. Poly(vinyl alcohol) (PVA) hydrogels possess several chemical properties that make them well suited for biomedical applications. These include inertness and stability, biocompatibility, and pH-responsiveness. As a result, PVA based materials have been studied for potential applications in areas of biomedicine such as targeted drug delivery, tissue engineering, and wound healing. This thesis examines the properties of PVA and seeks to understand how the chemical and physical structure affects their properties. It then examines how these properties enhance their utility in potential biomedical applications. Finally, it reviews the research into development of PVA based materials for three different biomedical applications.Chemical Engineerin

SciTech News Volume 71, No. 1 (2017)

Columns and Reports From the Editor 3 Division News Science-Technology Division 5 Chemistry Division 8 Engineering Division Aerospace Section of the Engineering Division 9 Architecture, Building Engineering, Construction and Design Section of the Engineering Division 11 Reviews Sci-Tech Book News Reviews 12 Advertisements IEEE

The accelerated characterization of viscoelastic composite materials

Necessary fundamentals relative to composite materials and viscoelasticity are reviewed. The accelerated characterization techniques of time temperature superposition and time temperature stress superposition are described. An experimental procedure for applying the latter to composites is given along with results obtained on a particular T300/934 graphite/epoxy. The accelerated characterization predictions are found in good agreement with actual long term tests. A postcuring phenomenon is discussed that necessitates thermal conditioning of the specimen prior to testing. A closely related phenomenon of physical aging is described as well as the effect of each on the glass transition temperature and strength. Creep rupture results are provided for a variety of geometries and temperatures for T300/934 graphite/epoxy. The results are found to compare reasonably with a modified kinetic rate theory

Effect of environment on mechanical properties of bagasse fiber reinforced polymer composite

In recent years the natural fiber composites have attracted substantial importance as a potential structural material. The attractive features of natural fibers like jute, sisal, coir and banana have been their low cost, light weights, high specific modulus, renewability and biodegradability. Natural fibres are lignocellulosic in nature. These composites are gaining importance due to their non- carcinogenic and bio-degradable nature. The natural fiber composites can be very cost effective material especially for building and construction industry. However in many instances residues from traditional crops such as rice husk or sugarcane bagasse or from the usual processing operations of timber industries do not meet the requisites of being long fibers. Bagasse contains about 40% cellulose, 30% hemicellulose, and 15% lignin. The present use of bagasse is mainly as a fuel in the sugar cane mill furnaces. It is felt that the value of this agricultural residue can be upgraded by bonding with resin to produce composites suitable for building materials. Keeping this in view the present work has been undertaken to develop a polymer matrix composite (epoxy resin) using bagasse fiber as reinforcement and to study its mechanical properties and environmental performance. The composites are prepared with different volume fraction of bagasse fibers. Experiments have been conducted under laboratory conditions to asses the effect of different environment such as subzero, steam, saline water and natural conditions on the mechanical properties of the composites. The change in weight, volume and dimensions are studied for various treatments. Shear strength of the composites was evaluated by three point bend test as per ASTM D2344-84. The volume fraction of composites having greater mechanical properties was taken for the second phase of experimentation. The second phase of experiment involves treatment of bagasse fiber with acetone and study of their environmental performance. The fibers were washed in soxhlet extractor. Micro structural examinations were also made to get an idea about the effect of treated and untreated fibers on the mechanical properties of the composites

Composite Structural Materials

The development and application of filamentary composite materials, is considered. Such interest is based on the possibility of using relatively brittle materials with high modulus, high strength, but low density in composites with good durability and high tolerance to damage. Fiber reinforced composite materials of this kind offer substantially improved performance and potentially lower costs for aerospace hardware. Much progress has been made since the initial developments in the mid 1960's. There were only limited applied to the primary structure of operational vehicles, mainly as aircrafts

An Assessment of Mechanical Behavior on High Temperature and Different Volume Fraction of Glass Fiber Reinforced Polymer Composites

Fiber reinforced polymer (FRP) composite materials are the primary choice in various structural and high performance application facilitating the need from the last four decades. High specific strength, high specific modulus, high stiffness to weight ratio, and design flexibility enables FRP composite materials to be used in a large number of critical structural components in aircrafts, satellite structures, various automobile components, wind turbine blades, sport goods etc. The mechanical properties of glass fiber/epoxy composite is significantly altered by high temperature and volume fraction which exhibits the various types of the failure modes (e.g. delamination sites, debonding, fiber pullout regions, crack propagation front, striations and bubble bursting in the matrix). The glass/epoxy composites were prepared for two different volume fraction of 50/50 and 60/40 and SBS samples were thermally conditioned at 500c at ambient and for different time duration period of 1hr, 5hr and 7hr. Interlaminar shear behaviour may be used to characterize FRP composite material.DSC analysis shows Tg value increases with increase in thermal conditioning time w.r.t ambient Tg value for glass/epoxy composites. From the FTIR analysis we observe the band at 550-650 cm-1 is the spectra range of 50/50 volume fraction of the glass/epoxy system with the shifting of bandwidth with decrease in thermal conditioning time

Bilayered chitosan-based scaffolds for osteochondral tissue engineering : influence of hydroxyapatite on in vitro cytotoxicity and dynamic bioactivity studies in a specific double-chamber bioreactor

Osteochondral tissue engineering presents a current research challenge due to the necessity of combining both bone and cartilage tissue engineering principles. In the present study, bilayered chitosan-based scaffolds are developed based on the optimization of both polymeric and composite scaffolds. A particle aggregation methodology is proposed in order to achieve an improved integrative bone–cartilage interface needed for this application, since any discontinuity is likely to cause long-term device failure. Cytotoxicity was evaluated by the MTS assay with the L929 fibroblast cell line for different conditions. Surprisingly, in composite scaffolds using unsintered hydroxyapatite, cytotoxicity was observed in vitro. This work reports the investigation that was conducted to overcome and explain this behaviour. It is suggest that the uptake of divalent cations may induce the cytotoxic behaviour. Sintered hydroxyapatite was consequently used and showed no cytotoxicity when compared to the controls. Microcomputed tomography (micro-CT) was carried out to accurately quantify porosity, interconnectivity, ceramic content, particle and pore sizes. The results showed that the developed scaffolds are highly interconnected and present the ideal pore size range to be morphometrically suitable for the proposed applications. Dynamical mechanical analysis (DMA) demonstrated that the scaffolds are mechanically stable in the wet state even under dynamic compression. The obtained elastic modulus was, respectively, 4.21 ± 1.04, 7.98 ± 1.77 and 6.26 ± 1.04 MPa at 1 Hz frequency for polymeric, composite and bilayered scaffolds. Bioactivity studies using both a simulated body fluid (SBF) and a simulated synovial fluid (SSF) were conducted in order to assure that the polymeric component for chondrogenic part would not mineralize, as confirmed by scanning electron microscopy (SEM), inductively coupled plasma-optical emission spectroscopy (ICP) and energy-dispersive spectroscopy (EDS) for different immersion periods. The assays were carried out also under dynamic conditions using, for this purpose, a specifically designed double-chamber bioreactor, aiming at a future osteochondral application. It was concluded that chitosan-based bilayered scaffolds produced by particle aggregation overcome any risk of delamination of both polymeric and composite parts designed, respectively, for chondrogenic and osteogenic components that are mechanically stable. Moreover, the proposed bilayered scaffolds could serve as alternative, biocompatible and safe biodegradable scaffolds for osteochondral tissue engineering applications